Consumer Price Index - CPI

What Does Consumer Price Index - CPI Mean?
A measure that examines the weighted average of prices of a basket of consumer goods and services, such as transportation, food and medical care. The CPI is calculated by taking price changes for each item in the predetermined basket of goods and averaging them; the goods are weighted according to their importance. Changes in CPI are used to assess price changes associated with the cost of living.

Sometimes referred to as "headline inflation".

Investopedia explains Consumer Price Index - CPI
The U.S. Bureau of Labor Statistics measures two kinds of CPI statistics: CPI for urban wage earners and clerical workers (CPI-W), and the chained CPI for all urban consumers (C-CPI-U). Of the two types of CPI, the C-CPI-U is a better representation of the general public, because it accounts for about 87% of the population. 

CPI is one of the most frequently used statistics for identifying periods of inflation or deflation. This is because large rises in CPI during a short period of time typically denote periods of inflation and large drops in CPI during a short period of time usually mark periods of deflation.